1. Field of the Invention
The invention relates to aback junction solar cell and a method of manufacturing the solar cell.
2. Description of Related Art
Solar cells are now expected to be a new energy source because of their capability to convert sunlight, which is clean and in unlimited supply, directly into electricity. The output of a single solar cell is only several watts. Accordingly, if solar cells are used as an electric-power source (energy source) for a house, building or the like, a solar cell module is used in which multiple solar cells are electrically connected together to increase the output.
There has been known a so-called back junction solar cell in which, for the purpose of expanding the light-receiving area, multiple lines of n type regions and multiple lines of p type regions are formed alternately on a back surface of a semiconductor substrate. A collecting electrode including a transparent conductive layer and a conductive layer is formed on each n type semiconductor region. This collecting electrode collects carriers (electrons) from the n type semiconductor region. Likewise, a collecting electrode including a transparent conductive layer and a conductive layer is formed on each p type region. This collecting electrode collects carriers (positive holes or acceptors) from the p type semiconductor region.
In general, each of the n type semiconductor region, the p type semiconductor region and the transparent conductive layer can be formed in a predetermined pattern by means of a metal mask (see, for example, Japanese Patent Application Publication No. 2005-101427). The use of metal masks has an advantage because high positional accuracy of the predetermined pattern can be achieved. Note that the conductive layer can be formed by a printing method or a sputtering method.
To improve the efficiency of collecting carriers, it is preferable to narrow the distance between each n type semiconductor region and the adjacent p type semiconductor region. To this end, slits are formed in the metal mask more densely. However, the metal mask with such a structure has a lower strength, and thus tends to have some portions broken or bent (raised). This may cause a problem of damaging the surface of the semiconductor substrate or misaligning the pattern. For this reason, there is a limitation to a microscopic formation of n type semiconductor regions and p type semiconductor regions by means of metal masks.
The invention has been made in view of the above-described circumstances and aims to provide a solar cell in which n type semiconductor regions and p type semiconductor regions are densely, microscopically formed, and to provide a method of manufacturing the solar cell.